The present invention relates to the method of improving the bondability in the package of integrated circuit (IC) fabrication, and more particularly to the method of improving the bondability between Au wires and Cu bonding pads in packaging ICs.
IC technology has produced dramatic advances over the past 20 years and already entered the sub-quarter submicron generation. The demand for progressively smaller, less expensive, and more powerful electronic products expedites the constant need for smaller geometry integrated circuits, and thus a denser packaging of circuits upon IC substrates. In discovering alternative metallization materials of satisfying the requirement, Cu is by far the most studied substitute for Al. Cu has higher resistivity and heavier atomic weight than Al. However, not like Al growing a passivating oxide in air and naturally protected against corrosion, AlCu alloys and Cu lines used in ULSI circuits have no passivating oxides, and thus they are more vulnerable to corrosion. Cu is electropositive and is relatively not vulnerable to electrochemical corrosion. However, the copper oxide in air increases linearly with time shows the lack of a protective oxide. The lack of a passivating oxide makes Cu more vulnerable to chemical corrosion. Furthermore, the copper oxides is a major factor effecting the bonding quality between Au wires and Cu bonding pads.
On the other hand, in addition to controlling variables of bonding such as bonding temperature, loads, and ultrasonic vibration magnitudes, the major concern in establishing high-quality, reliable wire bonding is the bondability between Au wires, which has been routinely used in packaging wiring, and bonding pads. Cu damascene is attractive for multilevel interconnection and being used in the industry. But due to the poor bondability (reaction) between Au wire and Cu pad, a solutions must be offered for packaging the chips with Cu top metal in wire bonding techniques; otherwise, it invites poor interconnections leading to degraded reliability.
Therefore, the constant effort in the industry is how to improve the bondability between Au wires and Cu bonding pads; however, there is still no breakthrough about this problem.
It is an object of the present invention to provide an improved method of increasing the bondability between Au wires and Cu pads in packaging of chip. It has been proposed that adding Al or AlCu (Cu up to 1%), which has long been demonstrated compatible with Au wiring, on Cu bond pad. By the methods of the present invention, Al or AlCu as a glue layer can be implemented on Cu bond pad for successful Au wiring. The bonding of Au wire and the bond pad of the chip with Cu top metal is improved.
One embodiment of the present invention further includes introducing a rough surface to the passivation layer, and thus creating the micro-topography which will promote the adhesion of the molding compound to the dielectric. Thermal coefficient expansion (CTE) of the molding compound then will not be so critical in the molding process.
Therefore, one object of the present invention is to provide a Al or AlCu layer upon the Cu bonding pads which acts as a protection layer of the Cu pads and a glue layer between Au wires.
Another object of the present invention is to provide an improved method for increasing the adhesion between the molding compounds and the surface of the passivation layer.
Further object of the present invention is to reduce the manufacturing steps and thus to decrease the complexity and cost.
According to the present invention, a method of improving the bondability between Au wires and copper (Cu) pads used in semiconductor manufacturing process, comprises: forming a Cu bonding pad on the top level of the metallization; chemical mechanical polishing (CMP) said Cu bonding pad; etching back said Cu bonding pad; depositing a barrier layer over said Cu bonding pad; and depositing AlCu or Al over said barrier layer to cover said Cu bonding pads.
According to the present invention, another method of improving the bondability between Au wires and Cu pads, used in semiconductor manufacturing process, comprises: etching a passivation layer to expose the underlying Cu bonding pads of the top level metallization; depositing a tungsten (W) barrier layer upon said Cu bonding pads; and depositing a Al layer on said W barrier layer.
According to the present invention, the method of improving the bondability between Au wires and Cu pads used in semiconductor processing comprises: forming a Cu bonding pad upon the top level metal; depositing a passivation layer over Cu bonding pad of the top level metallization; etching said passivation layer to expose said underlying Cu bonding pad through a contact window; depositing blanket aluminum (Al) on top of said barrier layer, performing Al CMP to remove Al on top of said passivation layer and leave Al only on the bonding pad of said contact window.
Other features and advantages of the present invention will be apparent from the accompanying drawings and from the detailed description that follows below.